Upon execution, the malware will attempt to spread through removable media using a time-based logic bomb, and overwrite the MBR (Master Boot Record) of all available drives after 40 days for variant A, and 20 days for variant B, making the host’s data inaccessible.

More info on the malware:

The worm uses two ways to spread – either via embedding in legitimate websites, in the form of a self-unpacking ZIP file or as an IQ test program, or via Exchangeable media, such as USB devices. The fact that it relies on USB devices to propagate is responsible for its rapid dissemination, which is likely to increase even further.

To date, the worm’s two variants - Win32/Zimuse.A and Win32/Zimuse.B differ in the method of spread and the timing of activation. While the A-variant needs 10 days to start spreading via USB devices, its B-variant needs only 7 days since infiltration. Moreover, the time needed for the execution of the destructive routine is shortened in the B-variant from the original 40 days to 20.